Contribution of functional genomics to identify the genetic basis of water-deficit tolerance in barley and the related molecular mechanisms

Drought, a major environmental constraint, has increasing impact on agricultural production. Genetic improvement for maintaining crop productivity in such adverse conditions is a critical challenge for breeders. Barley exhibits a remarkable genetic diversity associated with a widespread geographical distribution in contrasted climates. This diversity, which resides in regional landraces and wild accessions, has been only recently explored using functional genomics. Here, we review the data gained to identify in the barley germplasm collections, candidate genes participating in mechanisms conferring drought tolerance via signalling and protective mechanisms. We particularly focus on genes, for which QTL determination and association genetic-based mapping methods validate their likely roles in tolerance. Thus, allelic variants coding for transcription factors, heat shock or late embryogenesis proteins, and actors involved in ABA-signalling pathways, proline biosynthesis or redox regulation, have been characterized in wild and landrace populations, and constitute a solid basis for improving barley drought tolerance. The huge advance in sequencing technology and mass spectrometry, combined with the power of bioinformatics tools, makes it possible to envisage trials including a large number of genotypes to compare their physiological and biochemical features upon water deficit, and simultaneously determine the genetic basis of their differential behaviour. The implementation of such approaches will be powerful to identify promising loci for breeders for improving barley responses to drought.